1. Field of the Invention
This invention relates to a process for the production of glass-fiber reinforced plastics and resins, and more particularly to such a process using methyl methacrylate and a vinyl aromatic hydrocarbon as the primary and preponderant starting materials.
2. Description of the Prior Art
Glass-fiber reinforced plastics prepared from a starting material consisting of polymethyl methacrylate have been known in the past and are desirable for outdoor use, particularly in sheet-like form. Such glass-fiber reinforced plastics are prepared by impregnating glass fibers with so-called "methyl methacrylate syrup" obtained, for example, through partial polymerization of methyl methacrylate in a reaction vessel or through dissolution of polymethyl methacrylate in methyl methacrylate in a container, and then curing the impregnated glass fibers. Prior art production processes of this nature, however, suffer from the disadvantages that glass-fiber reinforced plastics obtainable thereby are inferior in transparency and that strength reduction resulting from poor weatherability is undesirably high. With regard to the inferior transparency in particular, studies made by the present inventors have revealed that the same results from too great a difference in refractive index between the glass fiber and the methyl methacrylate polymer; the refractive index of the glass fiber is 1.51-1.55 while that of the methyl methacrylate polymer is approximately 1.49.
Such facts are important especially when the glass-fiber reinforced resin is to be used, for example, as a flat or corrugated sheet which desirably has as superior a transparency as possible, since, in such cases, poor transparency results in substantially lowering the commercial value of the product. From this standpoint, it would be naturally expected that since a polymer of a vinyl aromatic hydrocarbon such as styrene has a refractive index of from about 1.58 to 1.60, glass-fiber reinforced plastics of superior transparency would be obtainable if methyl methacrylate and a vinyl aromatic hydrocarbon were copolymerized in an appropriate proportion to prepare a syrup consisting of a copolymer having the same refractive index as that of the glass fiber, and the glass fiber were impregnated with said syrup.
Extensive studies made by the present inventors have revealed, however, that even an attempt to partially copolymerize methyl methacrylate and a vinyl aromatic hydrocarbon and then to impregnate glass fibers with the resultant syrup followed by curing results in excessive time consumed in the cure process, further resulting in extremely reduced producibility and rendering such a production process impractical from the standpoint of industrial scale practice. It has also been found that in such cases an attempt to shorten the cure time, for example by the use of large amounts of initiators, will result in the reduction of initial strength of the resultant glass-fiber reinforced plastic and that further subsequent strength reduction due to poor weather-resistance is undesirably high. This tendency manifests itself significantly through the effects of heat, moisture, ultraviolet rays and the like, thus rendering the production process impractical. The phenomenon described above that the use of syrup obtained by copolymerization of methyl methacrylate and a vinyl aromatic hydrocarbon should result in lengthening the cure time to such an extent that the production process is rendered impractical thereby becomes fully apparent with the use of as little as 5% by weight, based on the methyl methacrylate, of the vinyl aromatic hydrocarbon, and the use of larger amounts of the vinyl aromatic hydrocarbon does not affect the phenomenon far beyond that when using 5% by weight.
On the other hand, when such monomers as methyl acrylate, ethyl acrylate and acrylic acid, which when combined with methyl methacrylate do not retard the polymerization rate compared to that of methyl methacrylate alone, are used together with methyl methacrylate, production of the glass fiber reinforced plastic can be carried out without prolonging the cure time as is not the case when using methyl methacrylate alone. However, when employing this method, the refractive index of the copolymer derived from the monomeric combination cannot be equalized with that of the glass fiber, it thus being impossible to produce glass-fiber reinforced plastics of good transparency.
It is therefore a primary object of the present invention to provide a glass-fiber reinforced plastic production process of high industrial value whereby the above enumerated disadvantages with respect to cure time, transparency and strength involved in the use of a syrup obtained by copolymerization of a combination of methyl methacrylate and a vinyl aromatic hydrocarbon can be overcome and excellent glass-fiber reinforced plastics can be produced with high efficiency and producibility.
Additional objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.